Si-H Activation in Titanocene and Zirconocene Complexes of Alkynylsilanes RC≡CSiMe2H (R=tBu, Ph, SiMe3, SiMe2H): A Model To Understand Catalytic Reactions of Hydrosilanes

Abstract

An agostic interaction between the Si–H bond and the metal center (depicted on the right) is the characteristic feature of the title complexes, which could be prepared by acetylene exchange reactions. IR, NMR, and X‐ray structural investigations reveal that the effect of the Si‐H‐metal interaction is considerably stronger at low temperatures and in the solid state. This mode of bond activation is important in active catalysts for hydrosilylation and dehydrogenative polysilane reactions.

Reactions of Hydrosilanes with Transition Metal Complexes and Characterization of the Products

“…20b Coordinated solvent can be replaced by η 2 -H-SiR 3 as illustrated previously in eq 64 as well as the displacement of coordinated THF by the "tethered" H-Si group in the HMe 2 SiCtCR complex of "Cp 2 Zr(THF)" to give 3-8. 139 A coordinated ClCH 2 Cl in [(OC) 3 L 2 M-(ClCH 2 Cl)] + (L ) P(OCH 2 ) 3 CMe] 2 ; M ) Mn, Re) and in [(OC) 4 L 2 Re(ClCH 2 Cl)] + was replaced by η 2 -H-SiEt 3 in the formation of 3-57, 3-62, and 3-63. 168,171 In the remaining examples in this section, addition of hydrosilane resulted in an increase in the electron count of an electronically and coordinatively unsaturated metal complex.…”

“…139 The M · · · H · · · Si interaction depicted by the authors resembled the composite structure shown in Scheme 15B as well as A in Figure 9 (for R ) SiMe 2 H). In the titanium case, it could be shown that bulky Cp ligands (Cp* and THI) provided sufficient steric hindrance to prevent the formation of the -agostic interaction.…”

“…The solid-state 13 C and 29 Si NMR spectra of Cp 2 Ti( t BuCtCSiMe 2 H) exhibited chemical shifts close to the values obtained for the lowtemperature solution data; thus, the structure for the solution (low temperature) should be similar to that determined by X-ray crystallography. 139 The corresponding isolated zirconium complexes exhibited similar features, although the 1 J (SiH) values were lower (68-86 Hz) and the ν(SiH) stretching frequencies were also more red-shifted and near ∼1700 cm -1 . A novel feature for Cp 2 M(HMe 2 SiCtCSiMe 2 H) (M ) Ti, 3-4; Zr, 3-9) was the presence of a single SiH resonance at ∼360 K in tol-d 8 , whereas at low temperature, two different Si-H bonds are detected: at 165 K, for M ) Ti the 1 J SiH(free) ) 186 Hz and the coordinated 1 J SiH ) 92, and at 246 K, for M ) Zr the 1 J SiH(free) ) 187 Hz and the coordinated 1 J (SiH) was 69 Hz.…”

“…This suggested a contribution of form B (Figure 9) and perhaps C, although the authors could not unambiguously prove OA of the Si-H from the low-temperature NMR data. 139 There are four similar complexes with a N-tether in which a -agostic interaction was proposed: Table 3, footnote 46). 155a The 1 J (SiH) values ranged from 97 to 129 Hz and, thus, were similar to the Ti complexes just described.…”

“…The NMR spectrum of a solution spectrum of Cp 2 Ti( t BuC 2 SiMe 2 H) in C 7 D 8 exhibited a resonance at 17.6 (193 K) and at -0.5 (303 K). 139 11 Additional derivative, Cp* 2 (HMe 2 SiCtCSiMe 2 H). 139 12 Uncoordinated SiH: 1 H (C 6 D 6 ), 4.47 (s, 1 J SiH ) 183).…”